How to Know Which Is the Hot Wire in a Two-Wire Plug

A two-wire plug uses a type A outlet. These outlets are the older version of the current type B outlet. Type B was created to provide a connection for an electrical safety system. The type A plug has two flat parallel prongs and can fit in both styles of outlets. The two prongs provide a hot and neutral electrical connection. Determining which wire is the hot connection is simple once you understand what to look for.

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Determining the hot wire in a two-prong plug can be done using one of two methods.

Visual Determination

Step 1

Hold the plug in your hand so you can inspect the two flat prongs.

Step 2

Determine which of the two prongs is wider than the other. This prong is the neutral connection.

Step 3

Determine which of the two prongs is narrower than the other. This prong is the hot connection. The wire connected to it is the hot wire.

Non-Contact Voltage Tester

Step 1

Lay the wire on a flat surface and cut the exterior sheathing off with a utility knife to expose the two wires inside. Be careful not to damage the insulated cover of the interior wires. Several small cuts is a better technique than one deep pass.

Step 2

Separate the two wires that are inside the cable by pulling them apart. Inspect the wires to double-check that you didn't compromise the insulation.

Step 3

Insert the plug into an outlet. Touch the non-contact voltage detector to each of the wires. When the detector illuminates or makes an audible sound, you have found the hot wire.